1. Field of the Invention
The present invention relates to a synchronizer, particularly to a synchronizer for a communication device and an access point.
2. Description of the Related Art
In a wireless WCDMA (Wideband Code Division Multiple Access) communication system, synchronization is an important procedure. When powered on, a mobile phone has to find out the optimal access point as soon as possible. With the popularization of the 3G system and the wireless network, a single device is usually required to work in the two systems. In South Korea, Japan, and Taiwan, the licenses of WCDMA and CDMA 2000 (Code Division Multiple Access 2000) are opened simultaneously. In such a condition, the 3G system should have the functions of WCDMA and CDMA 2000. Besides, the wireless network has been very popular now. Below is introduced the synchronization process of a WCDMA system and a CDMA system.
The synchronization process of a WCDMA mobile phone and an access point includes three stages each using a special channel to undertake synchronization. The three channels are the primary synchronization channel (P-SCH), the secondary synchronization channel (S-SCH), and the common pilot channel (CPICH). There are three types of data transmitted by the three channels: the primary synchronization code (PSC), the secondary synchronization codes (SSCs), and the scrambling code. A mobile phone just turned on does not know the timing of the frame and the slot of the channel until the mobile phone finds out the primary synchronization code. As there is none reference timing, the FIR (Finite Impulse Response)-based match filter is used to search for the related values. Then, the detection circuit is used to find out from 2560 chips the most probable chip where the slot initiates. After the synchronization of the primary synchronization channel is completed, the synchronization of the secondary synchronization channel begins. When the secondary synchronization code starts to be searched, the initiation times of all the slots have been known. Therefore, the active correlator is used to search for the secondary synchronization code. After the entire frame has been searched, a Comma-Free Reed-Solomon (CFRS) code is obtained. After the CFRS code is decoded, the frame boundary and the scrambling code group are obtained. The frame boundary and the scrambling code group can facilitate the active correlator to obtain the scrambling code sent out by the access point. The completion of the three stages of synchronizations is equal to the completion of the synchronization of the WCDMA system.
In a CDMA2000 system, the synchronization of an access point and a mobile phone uses the pilot channels. The pilot channels use a short pseudo noise code with a length of 32768 chips, and 512 chips can be issued therefrom. All the access points use the same pseudo noise code, but different access points transmit the pseudo noise code at different chips. The match filter is used to find out the initial value of the pseudo noise code and synchronize the mobile phone and the access point.
The de-correlation devices of the current DSSS (Direct Sequence Spread Spectrum) communication system are categorized into the match-filter circuit and the correlator circuit. Different systems use different DSSS codes and different synchronization circuits. Incorporating two communication systems in a single mobile phone should bring about some technical problems although it is the tendency.
To overcome the abovementioned problems, the present invention proposes a synchronizer for a communication device and an access point, which integrates the synchronization functions of the 3G mobile communication systems and advances the timing that the baseband chip enters the market.